1. Field of the Invention
This invention relates to a method for treating earthen formations which contain clay, shale or other fines to improve the flow of fluid through the formation. More particularly the invention relates to such a method wherein the decrease in the permeability of the formation upon contact with water is minimized and the permeability can even be increased.
2. Description of the Prior Art
Many earthen formations contain clays, shales, and/or fines, such as silt sized or smaller particles. The formation can be exposed at the surface of the earth, e.g., roadbeds, hillsides and the like, or it can be a subterranean formation, including both those just below or near the surface in which formations, footings or walls of structures rest, and those a substantial distance below the surface from which oil, gas or other fluids can be produced.
When contacted by water, water-sensitive clays and shales, for example montmorillonite, can swell and decrease the permeability of the formation. Other non-clay fines often are free to move and tend to be carried along with a fluid flowing through the formation until they become lodged in pore throats, i.e., the smaller interstices between the grains of the formation. This at least partially plugs the openings and reduces the permeability of the formation. Thus, finely divided particulate matter can obstruct flow through a formation by swelling, migration or both.
When footings or foundations of buildings rest in formations containing such fines, damage or at least great inconvenience often stems from the inability of the earth to carry away water due to decreased permeability of the formation when wet. Likewise, drainage of formations surrounding septic tanks and underlying roadbeds is desirable.
One common instance in which fluids are produced from or injected into formations is in connection with the production of oil. Often it is desired to treat oil-bearing formations to increase the amount of oil recoverable therefrom. One popular method is to inject steam into the formation The steam can be either dry or wet, i.e., it can contain a liquid water phase. In some instances steam is injected via a well, the well is then shut in temporarily and allowed to soak, and subsequently production is commenced from this same well. In other instances, steam is injected via one well and acts as a drive fluid to push oil through the formation to one or more offset wells through which the oil is produced. In either instance, when the steam reaches the subterranean formation, it at least partially condenses, thus exposing the formation rocks to fresh water. Even though the steam may act to mobilize the oil in the formation, if the formation contains fines and water-sensitive clays, the permeability of the formation can be so reduced as a result of the contact of the fines by the fresh water, the increase in oil production can be lower than expected, and, in some instances, production can even be lower than before the treatment.
In another instance a fines-containing subterranean formation penetrated by a well may require stimulation because of water damage which occurred during drilling or fracturing operations.
Various treatments have been proposed to stabilize clays in a formation. Such treatments include injecting into the formation solutions containing such materials as potassium hydroxide, sodium silicate, hydroxy-aluminum, organic acid chrome complexes, organic polymers and salts of a hydrous oxide-forming metal such as zirconium oxychloride. While each of these treatments has met with some success in particular applications, the need exists for a further improved method for treating a fines-containing formation to minimize the adverse affect of the fines on formation permeability, particularly when such a formation is contacted by a fluid containing water.
Therefore, it is a principal object of this invention to provide a method for reducing the permeability damage in and/or increasing the permeability of formations containing finely divided particulate matter due to passage of a fluid therethrough.
It is another object to provide a method for inhibiting permeability impairment due to migration, transformation and/or swelling of very fine particles within a porous formation.
It is yet another object to stabilize a formation containing water-sensitive clays, shale and other fines.
It is a further object to provide such a method wherein steam is injected into the formation.
It is a still further object to stimulate a formation which has been damaged by water.
Other objects, advantages and features of this invention will become apparent to those skilled in the art from the following description and appended claims.